A portable terminal apparatus such as a smart phone may have a wireless charging function. The portable terminal apparatus has a secondary battery and a circuit for charging the secondary battery therein with electronic power sent from a wireless charger. In order to carry out charging in a wireless manner, the portable terminal apparatus includes a power receiving coil, a power receiving circuit for receiving the electric power and a charging circuit for charging the secondary battery.
In wireless charging, the electric power may be transmitted through electromagnetic induction between a transmitting coil arranged in the wireless charger and the power receiving coil arranged in the portable terminal apparatus. Frequencies for transmitting the electric power are in a band of about 100 kHz˜200 kHz.
Also, a near field radio communication technology called NFC (Near Field Communication) is used for transmitting data in a wireless manner. The near field radio communication technology carries out transmission of data between a transmission apparatus and the portable terminal apparatus at a distance equal to or less than about 10 cm.
The NFC in a band of 13.56 MHz may be used. Communication is carried out by using electromagnetic induction between an antenna for communication arranged in the transmission apparatus and an antenna for communication arranged in the portable terminal apparatus. A communicable distance of the NFC may be as short as about 10 cm. The NFC generally carries out communication when the portable terminal apparatus is held over, placed on or placed close to the transmission apparatus.
A portable terminal apparatus may be equipped with both the wireless charging function and the NFC function. As noted, frequencies for wireless charging are 100 kHz˜200 kHz, and frequencies for NFC is 13.56 MHz, which are very different. As there is difference in the frequencies, the wireless charging and the NFC almost never interfere with each other. As there is no interference, it is possible to carry out data communication through the NFC while carrying out the wireless charging.
Another method of wireless charging that is different from the electromagnetic induction is based on magnetic field coupling using a frequency of 6.78 MHz. It is expected that the portable terminal apparatus including the wireless charging function corresponding to 6.78 MHz will increase in popularity. Even in the portable terminal apparatus using the magnetic field coupling of 6.78 MHz for wireless charging, the NFC of 13.56 MHz is likely to be used.
Many harmonic components are generated from a power transmission device for wireless charging using 6.78 MHz. In particular, a second harmonic is a 13.56 MHz, which coincides with the frequency of 13.56 MHz used in the NFC. Output for the wireless charging is very large (for example, around 10 W to several tens of W) compared to the output of the NFC for the purpose of transmitting the electric power. For this reason, if the portable terminal apparatus including the wireless charging function and the NFC function approaches the wireless charger, electric power with a large value that exceeds rating of an IC chip for NFC in the portable terminal apparatus is input. Because of the electric power exceeding the rating, there is a possibility that failure occurs in the IC chip for NFC and peripheral circuits thereof.